A communication system is formed, at a minimum, of a transmitter and a receiver interconnected by a communication channel. The communication system is operable at least to transmit communication signals, having an informational content, generated at, or applied to, the transmitter. The communication signals are transmitted to the receiver through the communication channel. The receiver is operable to receive the transmitted, communication signal and to recreate the informational content of the communication signal.
A radio communication system is a communication system in which the communication channel is formed of one or more frequency bands of the electromagnetic frequency spectrum. A transmitter operable in a radio communication system generates a communication signal of characteristics permitting its transmission through the communication channel, and the receiver operable in the radio communication system permits reception of the communication signal transmitted through the communication channel.
Typically, the radio receiver includes tuning circuitry tunable to the frequencies of the communication channel through which the communication signal is transmitted, down-conversion circuitry for down-converting a receive signal formed of the communication signal from a transmission frequency into a lower frequency signal, demodulation, and decoder circuitry which permit the informational content of the communication signal to be recreated.
A radio communication system is advantageous for the reason that a fixed, or hard-wired, connection is not required to form the communication channel extending between the transmitter and receiver. Communication can be effectuated between remotely-positioned transmitters and receivers without the need to form the hard-wired or other fixed connections therebetween.
A cellular communication system is a type of radio communication system. When the infrastructure, hereinafter referred to as the network, of the cellular communication system is installed in a geographical area, a subscriber to the cellular system is generally able to communicate telephonically in the system when positioned at any location in the geographical area encompassed by the system.
Cellular communication networks have been installed throughout significant portions of at least many of the world's population centers. Large numbers of subscribers to cellular communication systems formed of such cellular networks are able to communicate telephonically when positioned in areas encompassed by such cellular networks.
However, in some areas, such as areas not proximate to population centers, conventional, i.e., terrestrial, cellular communication networks have not been installed. In areas of low population density, for instance, a terrestrial-cellular communication network might not be commercially viable and is not installed.
The terrestrial-cellular communication networks which have already been installed have also been constructed pursuant to various different standards. A user terminal operable in one of the cellular communication systems is sometimes not operable in others of the cellular communication systems.
Therefore, even in an area in which a cellular communication network has been installed, a user might not be able to communicate by way of the cellular communication network if the user attempts to utilize a user terminal constructed to be operable only with another one of the cellular communication networks.
Satellite-cellular communication systems have been proposed which, when implemented, shall permit a user, utilizing a user terminal operable therein, to communicate telephonically by way of the satellite-cellular communication system when positioned at almost any location. By transmitting down-link and signals between a satellite-based transceiver and the user terminal and up-link signals between the user terminal and the satellite-based transceiver, telephonic communication shall be possible between the user terminal and the satellite-based transceiver. By effectuating additional communication links between the satellite-based transceiver and a ground station, the user of the user terminal shall be able to communicate telephonically with another party by way of the ground station and the satellite-based transceiver.
Numerous technical obstacles must be overcome in order to implement a workable, satellite-cellular communication system. For instance, the user terminal must be capable of transmitting communication signals to a satellite-based transceiver orbiting the Earth at a distance of perhaps thousands of kilometers above the Earth's surface.
Also, costs associated with placing the satellite-based transceiver in orbit are quite significant, and the satellite-cellular communication systems are being designed in ways to minimize the number of satellite-based transceivers required of such a system while still providing a worldwide coverage area. Supervisory communications between the satellite-based transceiver and a user terminal should therefore be minimized.
When a call is to be placed to a user terminal, for instance, supervisory communication signals are first transmitted to the user terminal. The user terminal must be informed of the call placement so that, inter alia, the user terminal can be tuned to a proper communication channel to receive and to transmit communication signals pursuant to the call.
To initiate the communications, a network station, either the satellite-based transceiver, or in a terrestrial-cellular communication system, a base station, transmits a paging signal to the user terminal. Repeated transmission of a paging signal might unnecessarily occur if the network station fails to receive timely indications of reception by the user terminal of the paging signal.
The paging signal must be of a "margin" great enough for the user terminal to detect the signal. The margin of the signal is the amount of power of the signal available to a receiver over a nominal level that permits adequate detection by the receiver of the signal over Gaussian noise levels. The margin of a signal is sometimes expressed in terms of decibels (dB) over a noise level. The margin of a signal can be increased by increasing its power level, by encoding the signal, and by repeating the signal. An acknowledgment signal can be generated by the user terminal to acknowledge its receipt of the paging signal. Analogous to the margin required of the paging signal, the acknowledgment signal must be of a margin great enough for the network station to detect the signal.
As the user terminal is of a limited power capacity, the power level of an acknowledgment signal transmitted by the user terminal to the network station cannot be increased indiscriminately to increase the margin of the acknowledgment signal. Therefore, when the communications must be effectuated upon a transmission channel exhibiting a high level of attenuation, the acknowledgment signal might not be able to be adequately communicated to the network station.
What is needed, therefore, is a manner by which to minimize the number of paging signals required to be transmitted by a network station to initiate communications between a network station and a user terminal. What is also needed, therefore, is a manner by which to acknowledge, with a high margin signal, reception of a paging signal at a user terminal.
It is in light of this background information related to communications pursuant to a radiotelephonic communication system, such as a satellite-based or terrestrial-based cellular communication system, that the significant improvements of the present invention have evolved.